Problem: Solve for $x$ and $y$ using substitution. ${-x+y = -7}$ ${x = -2y-11}$
Explanation: Since $x$ has already been solved for, substitute $-2y-11$ for $x$ in the first equation. ${-}{(-2y-11)}{+ y = -7}$ Simplify and solve for $y$ $2y+11 + y = -7$ $3y+11 = -7$ $3y+11{-11} = -7{-11}$ $3y = -18$ $\dfrac{3y}{{3}} = \dfrac{-18}{{3}}$ ${y = -6}$ Now that you know ${y = -6}$ , plug it back into $\thinspace {x = -2y-11}\thinspace$ to find $x$ ${x = -2}{(-6)}{ - 11}$ $x = 12 - 11$ ${x = 1}$ You can also plug ${y = -6}$ into $\thinspace {-x+y = -7}\thinspace$ and get the same answer for $x$ : ${-x + }{(-6)}{= -7}$ ${x = 1}$